The Sennheiser AB 3 Antenna Amplifier is for the Sennheiser Evolution Wireless G3 series. The AB 3 amplifier's bandwidth is 42 MHz, rather than the 36 MHz of the AB 2, which it replaces. Bandwidth, when talking about AB boosters, refers to the built-in filters in the unit. The Sennheiser AB 3 antenna head amplifier boosts the signal from a remotely mounted antenna wityh a long cable run, typically 50' or longer. Signal loss from a long cable can be high, and a booster overcomes that loss.